
Vanguard · magic (AP) damage
Sejuani is a Vanguard that deals magic (AP) damage and brings airborne, stun, slow. Some of their lockdown (airborne) ignores tenacity, so you dodge it; you can't cleanse or Merc' through it. Below is Sejuani's highest-win-rate build from high-elo games; open the counter-build tool to tune it against your specific enemy team.

After being out of combat, Sejuani gains Frost Armor which grants Armor and Magic Resist and immunity to slows. Frost Armor persists for a short time after Sejuani takes damage. Sejuani can damage a stunned enemy to shatter it, dealing massive magic damage.

Sejuani charges forward, knocking enemies into the air. The charge stops after hitting an enemy champion.

Sejuani swings her mace twice, dealing damage, slowing enemies and applying Frost stacks.

Sejuani freezes and stuns an enemy champion that has maximum Frost stacks.

Sejuani throws her bola that freezes and stuns the first champion hit and creates an ice storm that slows other enemies.
Q Arctic Assault
W Winter's WrathStuntenacity helpsFROM
P Fury of the North
E Permafrost
R Glacial PrisonSlowignores tenacityFROM
P Fury of the North
W Winter's Wrath
R Glacial PrisonHover a crowd-control type to see which ability it comes from.
Resolve
Grasp of the Undying
Aftershock
Guardian
Demolish
Font of Life
Shield Bash
Conditioning
Second Wind
Bone Plating
Overgrowth
Revitalize
Unflinching
Precision
Press the Attack
Lethal Tempo
Fleet Footwork
Conqueror
Absorb Life
Triumph
Presence of Mind
Legend: Alacrity
Legend: Haste
Legend: Bloodline
Coup de Grace
Cut Down
Last Stand

Based on 2767 games · 51.5% win rate · challenger+grandmaster+master+emerald-diamond+platinum-emerald · patch 16.18.1.
Resolve
Grasp of the Undying
Aftershock
Guardian
Demolish
Font of Life
Shield Bash
Conditioning
Second Wind
Bone Plating
Overgrowth
Revitalize
Unflinching
Sorcery
Summon Aery
Arcane Comet
Deathfire Touch
Axiom Arcanist
Manaflow Band
Nimbus Cloak
Transcendence
Celerity
Absolute Focus
Scorch
Waterwalking
Gathering Storm

Based on 359 games · 47.4% win rate · challenger+grandmaster+master+emerald-diamond+platinum-emerald · patch 16.18.1.
Resolve
Grasp of the Undying
Aftershock
Guardian
Demolish
Font of Life
Shield Bash
Conditioning
Second Wind
Bone Plating
Overgrowth
Revitalize
Unflinching
Precision
Press the Attack
Lethal Tempo
Fleet Footwork
Conqueror
Absorb Life
Triumph
Presence of Mind
Legend: Alacrity
Legend: Haste
Legend: Bloodline
Coup de Grace
Cut Down
Last Stand

Based on 79 games · 53.2% win rate · challenger+grandmaster+master+emerald-diamond+platinum-emerald · patch 16.18.1.
Resolve
Grasp of the Undying
Aftershock
Guardian
Demolish
Font of Life
Shield Bash
Conditioning
Second Wind
Bone Plating
Overgrowth
Revitalize
Unflinching
Precision
Press the Attack
Lethal Tempo
Fleet Footwork
Conqueror
Absorb Life
Triumph
Presence of Mind
Legend: Alacrity
Legend: Haste
Legend: Bloodline
Coup de Grace
Cut Down
Last Stand

Based on 66 games · 47% win rate · challenger+grandmaster+master+emerald-diamond+platinum-emerald · patch 16.18.1.